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©2017 Politecnico di Torino 1

Introduction to databases Web programming: the PHP language

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Web programming

The PHP language

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Our objective

Teaching you everything about PHP? Not exactly

Goal: teach you how to interact with a database via web

Access data inserted by users into HTML forms

Interact with a DBMS (MySQL in particular): connect to a database, execute a query, store the result of the query…

Access the tables returned by the DBMS

Assemble the HTML page on the browser, composed by HTML instructions and data extracted from the database



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Contents

Overview of the PHP language

Structure of a program

Variables and types (associative arrays)

Expressions and operators

Control structures (foreach)

Parameter acquisition from HTML forms

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What is PHP

Born in 1994

Personal Home Page, today known as PHP Hypertext Preprocessor

Created specifically for the development of dynamic webpages

Many useful resources, e.g.

http://php.html.it/guide/

http://www.web-link.it/php/

http://php.html.it/guide/






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Static webpages

Client Server

request message

HTML document

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Dynamic webpages

request message

program

parameters

HTML

document

program

reply

Client Server



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Primary goal

PHP‟s primary goal is to generate HTML code

In particular, generating HTML code by the results of an elaboration, that depend on the user input on the database contents, …

The PHP code is inserted inside the HTML code

The PHP code is executed on the Web server and the result (HTML and script result) is sent back to the browser

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Why using PHP?

Available for many platforms, different in

Hardware (Intel, Sparc, Mac, etc....)

Operative system (Linux, Unix, Windows, etc...)

Web server (Apache, IIS, IPlanet, etc...)

PHP code is “highly portable”

The PHP interpreter is Open Source

Free, wide availability of tools, support,developers, community of users

Pretty easy to learn, very simple if you already know C

Able to interact with various Database Management Systems (MySql, Postgres, Oracle, ...)



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First example

Text file with .php extension

// This is PHP code

Hello world!

Hello world!

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First example

If I look at the source code on the browser…

Why?

The browser shows the result of the execution of the PHP file, NOT the PHP file

Hello world!

Hello world!



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“Printing” strings

One of the most important (and frequent) tasks of PHP code is to create HTML code that will be displayed on the browser

echo and print constructs

Hello world! <

Hello world!

Hello world!

Hello world!

// They all produce the same output

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A quick digression: XAMPP

XAMPP is a cross-platform Apache distribution that includes:

A web server (Apache)

A database management system (MySQL/MariaDB)

PHP and Perl script interpreters

A graphical administrator of MySQL database (phpMyAdmin)

It can be used as a web-database development environment, thus making server-side scripts (e.g., PHP) and programs (e.g., DBMS, Web server) work locally



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A quick digression: XAMPP

XAMPP installs all necessary software for the development and deployment of a local web site

The PC becomes client and server

The Apache web server automatically creates a virtual domain (with local validity) at the localhost address (http://127.0.0.1)

Being connected to the Internet is not needed to use XAMPP

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XAMPP : DB administration

Allows to manage databases

Graphical interface

http://127.0.0.1/



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Tags to include PHP code

PHP code can be insterted in any point of a HTML page

Needs to be enclosed by tags

Hello world!

Hello world!

Hello world!

// This is PHP code

// This is PHP code

// This is PHP code

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Another example

Display the current date

In a static way

And tomorrow?

In a dynamic way

Updates in real time

// dd/mm/aa format



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Code analysis

In a script we use

Comments: //………

Variables: $today

Operators and language constructs: echo

Functions: date()

// dd/mm/aa format

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Variables

A variable is a symbol or a name that represents a value

A variable can represent different types of value

Integer number, real number, character, …

The data type can change during the execution of the program

When a program is executed, variables are replaced by real data

The same program can elaborate different types of data sets in this way



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Variables

In PHP the name of variables is preceded by the dollar symbol („$‟)

PHP does not require that variables are declared before their usage

Higher flexibility with respect to other programming languages

”The result of the operation (9 * 4) is: “;

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Data types

PHP supports different data types

Boolean: true or false

Integer: decimal numbers

Float: floating point numbers

String

Array

Object

Resource

Data types don‟t need to be set by the programmer but they are automatically detected by the PHP intepreter



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Strings

A string is a sequence of characters, with no length limitation

Included between a couple of single or double quotes

If double quotes are used (""), the string content gets expanded (or, technically, "interpolated")

The number is

The number is 10

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Arrays

An array is a complex variable that contains a series of values, each of them characterized by a key (or index) that unambiguously identifies it

PHP supports both scalar and associative arrays

Scalar arrays identify each element with its position number in a sequence

Associative arrays identify each element with a key in an univocal way



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Arrays

Example of a scalar array

Example of an associative array

The key can be a string or an integer

(„white‟, „black‟, „yellow‟, „green‟, „red‟); $colors

$colors

$colors

// prints „black‟

// prints „red‟

“name”

“name”

“surname”

prints prints

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Arrays

Multidimensional arrays are possible

"name"

"surname"

"name"

"surname"

prints

"first"

"second"

"second"



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Arrays

Array elements can also be heterogeneous

In PHP it‟s very easy to add or remove elements of an array

"hello"

// adds an element to the first available position

// adds an element on the specified position

// Error!!! (The element does not exist)

// removes the specified element

// removes the entire array );

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Arithmetic operators

// addition

// subtraction

// multiplication

// division

// module (division remainder)

// increment $x by 4 (equivalent to $x = $x + 4)

// decrement $x by 3 (equivalent to $x = $x + 3)

// equivalent to $x = $x / 5

// equivalent to $x = $x * 4

// equivalent to $x = $x % 3

// increment by 1

// increment by 1

// decrement by 1

// decrement by 1



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Logical operators

Comparison operators

// logical and

// logical or

// logical xor

// logical not

// equal

// not equal

// greater

// greater or equal

// less

// less or equal

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String operations

Concatenation

Example

prints

prints prints

prints

// the value of string $a is concatenated to string $x

// equivalent

$Name

$Name

$Name

$Name

"$Name

$Surname

$Surname;

$Surname"

$Surname;

$Surname



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Control structures

Allow the conditional execution of parts of the program

Allow the iterative execution of parts of the program

Evaluate certain conditions

PHP control structures

if, if..else, if..elseif

switch

while, do..while

for

foreach

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Conditions

A condition is an expression that generates a boolean value (true or false)

They use comparison operators and Boolean operators

The following values are equivalent to “false”

The Boolean value false

The integer number 0 and the real number 0.0

The empty string (“”) and the “0” string

An empty array

Each other value is considered true



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The IF construct

If the condition expressed by the IF block is true, the piece of code is executed

?

X

A

Y

T

F

is equal to , they are

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The IF .. ELSE construct

If the condition expressed by the IF block is true, the sequence of operations follows the THEN branch, otherwise the ELSE branch

? T F

X

A

Y

B



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The IF .. ELSE construct

If the condition expressed by the IF block is true, the sequence of operations follows the THEN branch, otherwise the ELSE branch

is equal to , they are

echo “\$a is different from \$b. \n\$a equals \”$a\” while \$b equals \”$b\”.\n”;

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The IF .. ELSEIF construct

Allows to choose among many options

1

2 A

X

Y

B

T F

T F

C

is equal to

is greater than

is less than



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The switch construct

Allows to predict different possible values for an expression and to execute specific code according to the value

Replaces a series of IF

break: forces the exit from the switch block

default: is optional

($name)

„Luke‟:

„George‟:

„Frank‟:

“Hello, my old friend!”;

“Hello,

“Nice to meet you, Paolo”;

“Welcome, whoever you are”;

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The while loop

The block of instructions inside the while gets executed until the condition stays true

It‟s possible that the cycle is never executed, in case the condition is false from the beginning

In general the block of instructions modifies the parameters used in the condition

?

X

A

Y

T F



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The while loop

The block of instructions inside the while gets executed until the condition stays true

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The do .. while cycle

Similar to the while, but it guarantees that the block of instructions is executed at least once

The condition is checked after the execution of the block of instructions



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The for cycle

Allows to repeat a block of instructions directly defining

The instructions of inizialization, executed only once upon entering the cycle

The condition, that, must be true to execute the block of instructions

The update, executed at the end of iteration

Can always be rewritten as a while loop

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The for cycle



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The foreach cycle

Cycle created to simplify access to arrays

Equivalent to a for cycle on the elements of an array

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The foreach cycle on associative arrays

January has 31 days.

February has 28 days.

March has 31 days.

April has 30 days.

May has 31 days.

June has 30 days.

July has 31 days.

August has 31 days.

September has 30 days.

October has 31 days.

November has 30 days.

December has 31 days.

“January” => 31,

“February” => 28,

"March” => 31,

“April” => 30,

“May” => 31,

“June” => 30,

“July” => 31,

“August” => 31,

“September” => 30,

“October” => 31,

“November” => 30,

“December” => 31);

($year as $month => $days) {

“$month has $days days.



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PHP and HTML forms

“form” tag with some attributes

Name: form name

Action: name of the program that will elaborate form data

Method: how parameters will be passed from the form to the program (can be "GET" or "POST")

Inside the form there are many input elements

“userData” “reponsePage.php”

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Access to form data

The destination PHP script accesses to user inserted values through some special variables calles “superglobal”: the associative arrays $_GET, $_POST and $_REQUEST

“Superglobal” variables are accessible even inside some potential functions

GET method

Values inside the query string are stored in the associative array $_GET

Each parameter of the form becomes a field of the associative array $_GET



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Access to form data

POST method

Each parameter of the form becomes a field of the associative array $_POST

The associative array $_REQUEST contains $_GET, $_POST and $_COOKIE

Even if it‟s not the same thing, in practice it can be used with any method, in alternative to $_GET or $_POST

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Example: GET method

"number"

"number"

"number"

Conference:

Conference:

Year: Year:

Articles:

Articles:

"year"

Insert data

"Delete" "Send"



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Example: GET method

File test.php

In the year 2006 you presented 2 articles to the ICSE conference.

“year”

Result

“number”

echo “In the year $year you presented $num articles to the”;

echo “$conf conference.”;

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Example: calculator

Result: 2.5

Calculator

value=“Delete”>

value=“Calculate”>



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Example: calculator

File calculator.php

Result

Not a number!</h3></font>‟;

Division by zero!</h3></font>‟;

// Input data checking

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Example: calculator

// Execution of the requested operation

// Visualization of the result

Result”



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Example: multiple choice

You know the following 3 programming languages

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HTML form

Uses the langs[] array instead of 6 variables

“Send”

Which of the following programming languages do you know?



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PHP script

The $_REQUEST ["langs"] array contains all selected values (in this case C, Perl and PHP)

You know the following 3 programming languages

$languages

$languages $value $value

echo "<p>You know the following $num programming languages<ul>";

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